and Overhead Unit. To eliminate the possibility of a
`similar latent software error in the System Monitor
`and the Control Law Processor, a dissimilar set of
`algorithms are
`implemented in System Monitor
`software.
`
`the System Monitor assesses
`As a second function,
`the approach progress and annunciates a caution to
`the crew if the approach exceeds limits which could
`cause
`a
`landing outside
`the desired touchdown
`footprint.
`
`3. System/Crew Interface and Crew Procedures
`
`The ability of the pilot not flying (PNF) to monitor
`the progress of the approach through the initiation of
`flare while remaining head down was a primary
`consideration during system design.
`The following
`information provided to the PF on the HUD is also
`provided on the PNF instrument panel
`to ensure
`awareness of system status and approach progress.
`
`1. An annunciator indicating system readiness to
`execute a CAT III approach (AIII status).
`which
`2. An
`Approach
`Warn
`indicator
`annunciates
`a
`system malfunction or
`an
`approach flown outside required limits.
`3. An expanded localizer display at the bottom of
`the ADI with
`indicated limits
`equal
`to
`localizer limits on the HUD.
`4. The vertical guidance command which the PF
`is following on the HUD is repeated head down
`for the PNF to enable him to evaluate pilot
`tracking
`performance
`below the
`altitude
`where
`glideslope
`information
`becomes
`unusable.
`
`the PNF are I) assisting in
`Two other duties of
`performing the approach checklist and 2) executing a
`go-around in case of a HUD system failure. Prior to
`approach initiation,
`the approach course, airspeed,
`field elevation and glideslope angle are entered
`through the Captain's panel
`instruments and HUD
`Control Panel.
`By initiating a system test,
`these
`values are displayed on the HUD, and then read L.
`the PF and cross—checked to the approach plate by
`the PNF. Below 500' the PNF rides passively on the
`controls; one hand on the wheel and the second
`behind the throttles.
`A "go-around your controls‘
`call by the PNF gives control of the aircraft to the
`PNF. He will take control without direction only on
`loss of
`response by the PF in a response exchange
`initiated prior to decision height.
`
`4. Aircraft Installation Drawing Package
`
`To ensure consistency and repeatability of system
`installation
`a
`detailed
`drawing
`package was
`developed prior
`to intial aircraft
`installation and
`revised during installation on the two flight
`test
`aircraft. Achieving system separation on the aircraft
`in order
`to prevent
`loss of critical
`information to
`both the Captain and First Officer in the event of a
`wire bundle overheat or serious avionics malfunction
`required rework of existing aircraft wiring in the
`form of physical wire separation or sleeving where
`separation was not possible. A document describing
`the wire
`separation objectives and methods was
`prepared and approved by the FAA prior to system
`installation in the No. 2 aircraft.
`
`detailed
`contains
`also
`package
`drawing
`The
`operational
`test
`an
`instructions,
`installation
`interconnect
`to all
`procedure to ensure a proper
`avionics systems and a compatibility test to ensure
`non-interference with other aircraft systems.
`
`5. Safety and Failure Analyses
`
`safety
`the
`system to meet
`the
`The ability of
`requirements for operation in CAT 111 conditions was
`established and verified by conducting three separate
`analyses
`each
`resulting in
`extensive
`supporting
`documentation.
`
`The System Safety Analysis considered the ability of
`the
`system to ensure
`that
`the
`probability
`of
`undetected hazardous events were on the order of
`one part in 10 ‘8.» The following hazardous events
`were included in the analysis:
`long landing, short
`landing,
`landing laterally off
`the
`runway, hard
`landing, wing tip strike. and nose wheel strike. The
`conditions which could lead to these events were then
`examined. Once the causes of each hazardous event
`were
`identified,
`fault
`trees were constructed in
`accordance with guidelines set forth in "Fault Tree
`handbook"(5). The known failure rates of sensors and
`the predicted failure rates of the HUD system were
`used
`along with
`predicted
`exposure
`times
`to
`determine,
`in accordance with the fault
`trees,
`the
`probability of occurrence of the hazardous events.
`
`and Effect Analysis
`The System Failure Mode
`supported the Safety Analysis by establishing the
`failure rates and modes at the avionic unit level. The
`Detailed FMEA considered HUD System faults at the
`component level to support the system level analysis
`and to verify predicted built-in-test and monitoring
`effectiveness.
`In addition a failure test plan was
`prepared and tests were conducted to verify the
`detailed analysis.
`
`6. Simulation and Flight Test Plans
`
`A three axis motion simulator with visual scene was
`employed to develop the pilot
`system interface,
`evaluate pilot control response and to determine the
`ability of
`the system with the pilot—in-the-loop to
`meet
`touchdown
`footprint
`requirements
`in
`the
`specified environment.
`Prior
`to evaluating the
`system on the motion simulator the HUD Guidance
`System,
`airborne
`sensors,
`target
`aircraft
`aerodynamics, ground based lLS and environmental
`conditions were modeled and installed on a SEL 32/27
`computer
`system.
`A pilot model(3) was
`also
`developed to permit complete modeling of
`the lLS
`capture, approach,
`flare and touchdown.
`All
`the
`sensor models and the ILS model
`included bias, gain
`variation
`and
`noise
`contamination.
`The
`environmental conditions modeled included stearlv
`
`winds, wind shears, turbulence, runway slope, runway
`length. glideslope angle, pressure, and temperature
`variations.
`Probability
`distributions
`for
`the
`identified disturbances were developed and used to
`generate
`random environments
`for
`the model.
`Aircraft weight, center of gravity and approach
`speed, as well as the pilot model were adjusted in
`Monte Carlo fashion for statistical evaluation of the
`system design.
`
`environmental
`errors,
`sensor
`These
`and
`their
`configurations
`aircraft
`distributions were
`then applied to
`
`conditions,
`probability
`the manned
`
`444
`
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`
`Ex. 1031, p. 509
`
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`Ex. 1031, p. 509
`
`

`
`9. Aircraft Operation
`
`involved from the
`time
`length of
`to the
`Due
`beginning of CAT II flight tests to the completion of
`CAT Ill
`flights and the
`rising demand for 727
`aircraft,
`two HUD system and data acquisition
`installations were required on two separate aircraft.
`Uninterrupted operation of
`the aircraft
`proved
`difficult as we were low in the priorities of
`the
`maintenance organizations willing to assist a one-of-
`a-kind aircraft traveling the Northwest in search of
`the winds and weather needed to satisfy the flight
`test plan requirements. Because all aircraft landing
`and take-off operations align for
`the best wind
`advantage, and our mission was to explore adverse
`winds, we were unable to take advantage of numerous
`opportunities at Type II airports since this would
`mean working against the traffic flow. Air Traffic
`Control did accommodate our operations whenever
`possible permitting the completion of the flight tests.
`
`10.Simulation and Flight Test Data Confirmed Proof
`of Concept Test Results:
`
`The simulation and flight test programs confirmed
`that a man—in—the—loop control system, subjected to
`the
`environmental
`requirements
`for CAT
`111
`operations can meet, and in this case, exceed the
`requirements for autoland systems. Data plots for
`the simulator and flight test results are presented in
`Figures 6 and 7. Most of the simulation and flight
`test landings were made with the pilots vision of the
`outside world obscured.
`
`m:a¢.n :-.-
`rrrr
`
`uuocxwz
`Imcncuv
`
`zssu -
`VIE?
`
`rum
`rtst
`
` TOUCHDOWN
`
`DISPERSIONS
`NO. OF FLIGHTS
`
`988
`
`FIGURE 6
`SIMULATION DISPERSIONS
`
`testing techniques
`statistical hypothesis
`Classical
`were used to verify that
`the system performance
`dispersions met criteria set forth in AC 20-57A and
`AC 120-28C. Distribution fitting and extrapolation
`techniques combined with probability models of
`system monitor
`effectiveness were
`used
`for
`verification of
`low probability event
`statistics.
`Simulation statistics werelshown to be reliable by
`showing statistical equality of flight test results and
`simulator results.
`
`445
`
`BOEING
`
`Ex. 1031, p. 510
`
`correlation
`performance
`to establish
`simulator
`between the pilot model and a large number of
`subject pilots. A manned simulation test program was
`established to demonstrate system performance in
`the CAT Ill environment. The pilot group consisted
`of airline pilots and FAA pilots.
`Pilot variability
`proved to be
`a
`large contributor
`to touchdown
`dispersions. The FAA demonstration program in the
`manned simulator
`required over
`1000
`flights
`to
`touchdown.
`
`A flight test plan was then prepared to validate the
`fidelity of the simulation by demonstrating that the
`touchdown statistics from the simulation and the
`flight test were from the same population. The flight
`test plan required verifying performance in a subset
`of the environmental conditions used in the simulator
`demonstrations.
`
`7. Selection of Flight Test Crew
`
`this
`testing of
`the extensive flight
`To conduct
`experimental system in a large turbojet aircraft with
`the special requirement that some of the testing be
`done in actual CAT 111 weather, we developed special
`criteria for the selection of the crew and especially
`the chief pilot.
`The following requirements were
`applied in this selection.
`1. Previous experience in CAT 111 operations
`2. Previous experience in CAT 111 weather
`3. Previous R and D flight testing
`4. Ability to contribute to the development of
`operations procedures
`5. Ability to act as a right seat safety pilot
`
`We were fortunate to find an individual who could fill
`these roles well. We also received assistance from
`the FAA test pilots in a number of areas which
`helped make these tests successful.
`
`8. Development and Installation of the Flight Data
`Acguisition
`and
`Touchdown
`Verification
`Equipment
`
`the system in flight and at
`The performance of
`touchdown was gathered by a data acquisition system
`which received all
`the sensor data used by the HUD
`System, and stored this information on a high speed
`magnetic tape. An extensive data reduction system
`was then developed for the SEL 32/27 which provided
`time histories of sensor data, parameter/parameter
`plots and histograms across the flight test program.
`The system proved invaluable in determining aircraft
`and system performance, developing the final control
`laws, and in establishing the simulator flight
`test
`correlation.
`
`A belly mounted video camera was employed to
`verify aircraft
`touchdown position. With a wide
`angle lens and proper calibration, touchdown position
`could be established longitudinally within 20 feet and
`laterally within 2 feet.
`
`
`
`HUD symbology was continuously recorded on a
`second video system and overlayed with video from a
`forward looking camera mounted just behind the
`Windshield. This video system permitted the flight
`‘.351. engineers to view the approach as if they were
`sitting behind the HUD.
`
`
`
`BOEING
`Ex. 1031, p. 510
`
`

`
`2n -
`ru-r
`
`u.m::.c-¢
`wrmcor
`
`rs: u
`tn-1
`
`
`
`TOUCHDOWN
`DISPERS IONS
`NO. OF FLIGHTS
`
`107
`
`FIGURE 7
`
`FLIGHT TEST DISPERSIONS
`
`Conclusions
`
`the
`the HUD System to meet
`ability of
`The
`been
`requirements
`of CAT 111
`operations
`has
`examined:
`1) in Proof-of-Concept testing where the
`effectiveness
`of
`single HUD pilot
`in—the—loop
`operations was demonstrated; 2)
`in simulation where
`performance and limit
`requirements were tested;
`3) in the flight test aircraft where actual operations
`and correlation with simulation were demonstrated;
`and 4) in the engineering laboratory, simulation and
`aircraft where
`system failure modes have been
`analyzed, tested, and demonstrated. The issuance of
`the STC waits final review of reports and data and a
`test flight in actual weather conditions. This flight is
`scheduled for November of this year, 1981+, when low
`visibility conditions occur on the U.S. West Coast.
`
`this program is credited to the
`success of
`The
`assiduous design, development and test effort put
`forth by the staff at FDI,
`the assistance of our
`knowledgeable consultants and able flight crew, and
`the cooperation and support of the dedicated people
`of the FAA.
`
`(ALS)",
`
`(1) "Criteria For Approval Of Category Ill Landing
`Weather Minima",
`FAA
`Advisory Circular
`Number: l20—28C
`Systems
`(2) "Automatic
`Landing
`Advisory Circular Number: 20-57A
`(3) D.T. McRuer and E. S. Krendel, "Mathematical
`Models
`of
`Human
`Pilot
`Behavior",
`AGARD-AG-188: Jan., 1984
`"A Systems
`(4) McRuer,
`Jex, Clement, Graham,
`Analysis Theory for Displays in Manual Control",
`STI Tech Rpt No. 163: June 1968
`(5) McRuer, Ashkenas, Graham, "Aircraft Dynamics
`and Automatic Control", Princeton University
`Press: 1973
`
`FAA
`
`(6) Roberts, Vesely, Haasl, Goldberg, "Fault Tree
`Handbook", NUREG-0492: Jan., 1981
`
`446
`
`BOEING
`
`MR’?
`
`Ex. 1031, p. 511
`
`BOEING
`Ex. 1031, p. 511
`
`

`
`SESSION 15
`
`COMMUNICATION,
`
`NAVIGATION, AND
`
`IDENTIFICATION (CNI)
`
`TERMINALS
`
`Chairmen:
`
`Dr. Duncan B.Cox, Jr.
`Charles Stark Draper Lab, inc.
`
`Frank W. Smead
`ITT Avionics
`
`This session is primarily concerned with technical descriptions of actual or p/armed 0n—a/rcraft CN/
`termina/s and with the issues andbene/its associated with integrating several CNI functions together
`in one terminal.
`
`BOEING
`
`Ex. 1031, p. 512
`
`BOEING
`Ex. 1031, p. 512
`
`

`
`BOEING
`
`Ex. 1031, p. 513
`
`BOEING
`Ex. 1031, p. 513
`
`

`
`Pages 447-453 have been deleted intentionally.
`
`BOEING
`
`Ex. 1031, p. 514
`
`BOEING
`Ex. 1031, p. 514
`
`

`
`84-2591
`
`AN EXPERIMENTAL AERONAUTICAL SATELLITE DATA LINK
`
`Samuel Anderson
`
`Technical Staff
`The MITRE Corporation
`1820 Dolley Madison Boulevard
`McLean, Virginia 22102
`
`Abstract
`
`There is a need to improve communication and sur-
`veillance capabilities in oceanic airspace.
`In
`October 1982, The MITRE Corporation initiated a
`3-year, internally-funded project to design, deve-
`lop, and demonstrate an experimental aeronautical
`satellite data link system to provide data commu-
`nications capability between the ground and air-
`craft flying in oceanic airspace.
`
`This paper describes the approach used by MITRE
`in developing the system and presents technical
`details
`to support
`specific design decisions.
`The experimental aircraft data terminal
`is de-
`signed
`to provide
`low-capacity
`data
`transfer
`between the aircraft and an earth station via
`satellite.
`The
`low aircraft
`terminal data rate
`of
`200 bits per, second
`(bps) minimizes
`power
`requirements
`and thereby the costs.
`The
`link
`between the aircraft and satellite is at L-band
`(1.5/1.6 GHz),
`and
`the links between satellite
`and earth stations are at C-band (4/6 GHz).
`
`The subsystems comprising the aircraft data ter-
`minal
`include the transceiver, modem, processor,
`frequency control, and power. Digital logic func-
`tions are designed using STD Bus technology.
`The
`antenna design takes into account performance and
`cost
`tradeoffs between antenna gain and signal
`power.
`
`The system concept avoids the high cost of laun-
`ching, operating, and maintaining dedicated sat-
`ellites through sharing of existing commercially
`available satellite links (e.g.,
`INMARSAT) with
`other mobile users (e.g., maritime).
`The diver-
`sity among aeronautical users relative to their
`operational
`requirements and financial
`resources
`is
`accommodated
`by
`adopting a modular design
`architecture for user equipment
`that allows for
`expansion of capabilities at user discretion.
`
`Background
`
`The use of satellite channels has been considered
`since the early 1960s as an effective means of
`providing communications to a large group of aero-
`nautical users.
`For
`some applications,
`such as
`communicating to and from aircraft flying remote
`routes, out of the range of ground-based VHF sta-
`tions, satellite communication represents an ideal
`solution. Three satellites, correctly positioned,
`could conceivably provide coverage for all of the
`world's major air routes.
`The aeronautical satel-
`lite system concepts
`that have been studied to
`date, despite
`their
`theoretical
`and practical
`advantages, have been regarded as too expensive
`to be supported by aviation users, and none have
`been implemented.
`The cost of a satellite system
`dedicated to aeronautical users would involve the
`design and launch of satellites, earth station
`construction, maintenance, and technical support.
`
`The economic consensus regarding the high cost of
`dedicated satellite systems
`is clear, yet
`there
`remains a problem of inadequate aeronautical com-
`munications over oceanic routes. Although the
`sophistication of
`on-board aircraft navigation
`systems is increasing,
`there is as yet no reliable
`means of conveying the data produced by
`these
`systems
`to the ground (dependent
`surveillance)
`when the aircraft
`is beyond the range of
`radar
`and VHF radio links.
`
`committed large re-
`The MITRE Corporation has
`sources to the demonstration of a low-cost aero-
`nautical satellite data link, which will use a
`space segment of an already existing satellite
`system.
`The purpose is to show that aeronautical
`satellite communications need not be overwhelmr
`ingly expensive while being of great value to the
`aviation community.
`
`is based on analyses and conclusions
`The concept
`contained in an FAA report titled:
`"Oceanic Area
`System Improvement Study (0ASIS)."[l] An OASIS
`working group estimated that reduced minimum air-
`space requirements in the North Atlantic, made
`possible by an automatic dependent surveillance
`capability derived from the shared use of
`the
`International Maritime Satellite (INMARSAT)
`sys-
`tem, could generate an overall cost
`savings of
`from 90 to 164 million dollars in the time period
`between 1979 through 2005, depending on the speci-
`fic implementation.[2]
`An attractive feature of
`an INMARSAT-based aeronautical data link system
`is that aviation usage of the service could expand
`in increments. Beginning with limited satellite
`capacity initially,
`enough
`to
`serve
`selected
`applications,
`the user
`investment need increase
`only as existing demand and requirements increase.
`
`The MITRE experimental data link will consist of
`one aircraft terminal and one earth-station termi-
`nal, which will operate over a shared-space seg-
`ment of the present INMARSAT system.
`The aircraft
`terminal has been designed to provide a two-way
`communications link between the aircraft and the
`satellite at
`the existing maritime L-band mobile
`satellite
`frequencies
`(1.5/1.6
`GHz).*
`(See
`Figure 1.) Both hardware and software have been
`developed to provide for multiple access, modula-
`tion and coding, and antenna switching.
`
`Design Considerations
`
`Cost Factors
`
`It is not
`
`likely that an aeronautical satellite
`
`*When the aeronautical mobile
`satellite frequen-
`cies are made
`available in the subsequent gener-
`ations of the
`INMARSAT system,
`the aircraft ter-
`minal frequencies would also change correspond-
`ingly.
`The power budget given in Table
`2 is
`based on
`the second generation INMARSAT space-
`craft.
`
`Copyright © American Institute of Aeronautics and
`Astronautics, Inc., 1984. All rights reserved.
`
`454
`
`BOHNG
`
`Ex.1031,p.515
`
`BOEING
`Ex. 1031, p. 515
`
`

`
`UPLINK — 6.42 CH2.
`_
`0 GHZ
`nowNLINK
`4.2
`
`_
`
`ImumsAT
`MARECS "A" SATELLITE
`
`FORWARD ~ 1.54 GHz
`_
`64 CH
`RETURN
`1.
`Z
`
`TO SATELLITE
`
`FORWARD
`
`RETURN
`HGA ON HGA OFF*
`
`AIRBORNE
`
`DATA LINR
`TmNmAL
`
`
`
`1200 BAUD
`MODEM
`
`
`
`TELEPHONE
`LINE
`
`1200 BAUD
`MODEM
`
`MITRE
`DEMONSTRATION
`FACILITY
`
`
`
`
`ARRA
`PROCESSOR
`
`
`
`
`éfi¥§:fi;Y
`5
`
`EARTH STATION
`
`FIGURE1
`MITRE EXPERIMENTAL
`AERONAUTICAL SATELLITE DATA LINK
`
`data link design will be accepted unless it can
`be
`shown to be cost effective. This
`fact, when
`considered in a design perspective, places inevi-
`table constraints on system performance.
`The cost
`of an implemented service would depend primarily
`on two parameters, described below, both of which
`have a first-order effect on the overall cost.
`
`The subscription rates
`1. Earth Station Power.
`charged to users of
`a satellite system such as
`INMARSAT are based on the effective isotropic ra-
`diated power
`(EIRP)
`required from the satellite.
`For a given user channel,
`the satellite EIRP de-
`pends on the earth station transmitter power lev-
`els allocated to the specified channel and the
`gain provided by the satellite transponder.
`The
`aeronautical data link satellite EIRP requirement
`depends on several design variables such as data
`rate, aircraft antenna gain, and coding gain. Ex-
`pected link signal and power parameters
`for
`the
`proposed MITRE concept are given in Tables 1 and 2
`for
`the
`second
`generation
`INMARSAT
`space-
`craft.[3—5]
`
`IODULATION
`
`DPSK
`
`FREQUENCY (caz)
`TRANSMIT EIRP (dBW)
`FREE SPACE LOSS (dB)
`PROPAGATION MARGIN (dB)
`RECEIVE G/T (dB/K)
`C/No UP (dBHz)
`FROM SATELLITE
`
`6.42
`66.0**
`200.9
`1.7
`-14.0
`78.0
`
`FREQUENCY (GHz)
`SATELLITE EIRP (dBW)
`FREE SPACE LOSS (dB)
`PROPAGATION MARGIN (dB)
`ECEIVE G/T (dB/K)
`C/N0 DOWN (dBHz)
`
`1.54
`24.0**
`188.5
`5.0#
`-26.0##
`33.1
`
`C/No INTERMOD (dBHz)
`C/No TOTAL (dBHz)
`
`* The present generation MARECS-A satellite is
`equipped with a high-gain amplifier (HGA) pro-
`vided primarily for maritime
`search and rescue
`applications.
`The next
`generation INMARSAT
`satellites will be
`equipped with a high-gain
`amplifier that will operate in a portion of the
`aeronautical band as well.
`**Equivalent power of four INMARSAT maritime ser-
`vice voice channels.
`# Propagation margin includes fading,
`zation, and absorbtion losses.
`##Receive
`system noise temperature is assumed to
`be 500° K and the antenna gain is assumed to be
`1.0 dB.
`
`polariza-
`
`TABLE 2:
`
`LINK PARAMETERS AT 5° ELEVATION ANGLE
`
`The single aircraft-
`2. Aircraft Terminal Cost.
`terminal cost
`should include hardware and soft-
`ware,
`installation, antenna(s),
`and maintenance
`costs.
`
`Capability Tradeoffs
`
`in the
`compromise
`The first
`System Capability.
`design of a low-cost data link is a restriction
`on channel capacity.
`The channel capacity of the
`system, or the achievable data rate, is a function
`of the satellite EIRP for both the ground-to-air
`(forward)
`and
`air-to-ground
`(return)
`links.
`Therefore, data rates must be restricted in order
`to (l) avoid high service charges for the forward
`link,
`(2) minimize the cost of the power amplifier
`in the aircraft terminal transmitter on the return
`link, and (3) minimize the cost and complexity of
`signal processing electronics.
`It
`is clear
`that
`unless there is a revolutionary breakthrough in
`digital voice encoding,
`the proposed data link
`will not
`have
`sufficient
`capacity to provide
`voice communications (1,200 to 32,000 bps).
`
`The experimental data link has been designed to
`handle the data rates required for air traffic
`control
`(ATC)
`and automatic dependent
`surveil-
`lance functions as derived in the OASIS report.
`Automatic dependent surveillance of air traffic
`relies on navigational position data generated on
`board the aircraft
`and automatically communicated
`
`455
`
`BOHNG
`
`Ex.1031,p.516
`
`Eb/No (BER = 10-5)
`CONVOLUTIONAL CODING
`
`CODING IMPROVEMENT
`IMPLEMENTATION MARGIN
`DATA RATE
`REQUIRED cARRIER—To—NoIsE
`DENSITY RATIO (C/N0)
`
`10.4 dB
`1/2 rate,
`Constraint length-6
`3.5 dB
`2.5 dB
`200 bps
`
`32.4 dBHz
`
`
`
`TABLE 1:
`
`SIGNAL PARAMETERS
`
`BOEING
`Ex. 1031, p. 516
`
`

`
`sets‘
`
`Independent surveillance
`to ATC ground stations.
`describes
`surveillance methods which do not
`require
`such
`aircraft-generated
`data
`(e.g.,
`radar).
`The
`average
`network
`data
`throughput
`requirement
`for North Atlantic
`air
`traffic
`through the year 2005
`(223 in-flight aircraft)
`has been projected to be
`200 bits per
`second
`(bps) over the forward link and 700 bps over
`the
`return link.[l]
`The return link capacity can be
`divided between
`four
`channels,
`each having a
`200 bps capacity.[2]
`
`power
`In addition to lowering required signal
`levels,
`the use of low data rates takes advantage
`of
`the availability and
`low cost
`of micro-
`electronics,
`i.e., microprocessors
`that
`can
`handle most signal processing and encoding tasks
`when
`the
`data-rate-to-microprocessor-clock-rate
`ratio is low enough.
`It
`so happens that 200 bps
`approaches the upper data rate limit (400 bps may
`be achievable, but certainly nothing higher)
`for
`the type of microprocessor-based demodulator and
`error correction decoder
`implementations used in
`the experimental aircraft
`terminal design.
`(The
`experimental
`system operates at
`a standard data
`rate of 200 bps using 1/2 rate error-correction
`coding--2 channel symbols per information bit, or
`400 channel symbols per second--with 8-bit, 4 MHZ
`clock-rate microprocessor technology.)
`
`The Aircraft Antenna
`
`The aircraft antenna is a critical design feature
`because it plays a pivotal role in the data link
`cost
`tradeoff considerations.
`If,
`for a
`typical
`link power budget calculation, we assume a simple
`aircraft
`antenna with a hemispherical gain of
`+1 dBiC,
`the satellite L-band power
`required in
`the satellite-to-aircraft
`link is equivalent
`to
`approximately
`four
`INMARSAT maritime
`service
`voice channels.[2]
`On
`the other hand,
`if the
`aircraft antenna gain can be assumed to be some-
`what higher, on the order of +6 dBiC,
`then the
`equivalent
`power
`of
`slightly more
`than
`one
`INMARSAT channel is required. Another significant
`advantage of a higher gain antenna is that because
`the antenna's directional discrimination is great-
`er, channel degradation due to multipath interfer-
`ence is reduced.
`Probably the most sophisticated
`and best antenna for this application is a high-
`gain steerable phased array;
`however,
`a phased
`array does not represent an option in the aeronau-
`tical data link design being considered here be-
`cause such antennas are not currently available
`for what would be considered an acceptable cost.
`
`the optimum
`the imposed cost constraints,
`Under
`antenna configuration appears
`to consist of
`two
`microstrip antenna elements, flush-mounted on each
`side of the aircraft, approximately 40° down from
`top-center.
`Each antenna element provides a gain
`of at
`least +l dBiC over a 130° spherically sym-
`metrical angle,
`and much better gains at angles
`approaching vertical. Their optimum peak gain in
`the vertical direction,
`relative to the plane of
`the antenna element,
`is about +5 dBiC.
`For over-
`ocean communications
`in the North Atlantic,
`the
`dual,
`side-mounted antenna configuration should
`be able to exploit
`some of
`this directivity be-
`cause the one antenna element
`in use at any given
`time will be pointed in the general direction of
`the INMARSAT satellite for typical aircraft orien-
`tations and flight paths
`in the North Atlantic
`flight track system.
`
`The Aeronautical Multipath Channel
`
`The most complex technical
`The Multipath Problem.
`problem confronting the system design is the sig-
`nal degradation caused by the aeronautical chan-
`nel's multipath characteristic.
`A simple descrip-
`tion of multipath interference follows. When the
`direct-path satellite signal arrives at
`the air-
`craft antenna, it is accompanied by an assortment
`of
`reflected signals,
`varying
`in
`phase
`and
`intensity. Out-of-phase reflections add destruc-
`tively to the direct-path signal and cause fades
`whose durations
`and magnitudes vary randomly.
`The resulting interference to the desired signal
`is referred to as multipath interference.
`It
`poses a difficult problem because it cannot be
`overcome entirely by increasing transmitter power
`levels
`since the intensities of
`the
`reflected
`path signals would also increase proportionally.
`
`Overcoming Multipath Through Coding
`
`Error Correction Codes. Aside from using a high-
`gain antenna with good directional discrimina-
`tion, another way to contend with the multipath
`problem is by the use of error correction coding
`with interleaving. The theory of error correction
`codes
`is an extension of
`the well-known single-
`error-detecting parity check coding techniques.
`One
`significant difference
`in error-correction
`coding is that
`the quantity of
`redundant bits
`transmitted with the encoded message may vary
`from a small
`to a quite large percentage of
`the
`total message depending on the code
`rate used.
`The redundancy is exploited by the decoding algo-
`rithm to recover the original message from a re-
`ceived noise-corrupted encoded message if the num-
`ber of errors in the received message
`is less
`than some maximum defined by the code.
`
`Interleaving. Most error-correction codes are ef-
`ficient at correcting random errors; however,
`in a
`multipath environment,
`the errors caused by fading
`may extend over long groups of encoded
`symbols,
`called error bursts.
`To manage the decoding of a
`message with error bursts,
`interleaving is used.
`It is a technique that essentially randomizes the
`channel errors received by the error correction
`decoder.
`It
`is
`performed
`in the
`transmitter
`processor after
`the data has been encoded and
`prior to transmission over the channel.
`A block
`of encoded symbols are reordered such that symbols
`ordered
`consecutively before
`interleaving are
`interspersed in the channel symbol stream,
`sepa-
`rated by
`a
`number
`(equal
`to the
`interleaving
`depth) of similarly reordered symbols.
`At
`the
`receiver, after the deinterleaving process is com-
`pleted, channel burst errors appear
`to the error
`correction decoder as random, uncorrelated errors.
`
`Interleaved Convolutional Encodin /Viterbi
`Decoding.
`The error-correction code selected for
`the
`experimental aeronautical data
`link is
`a
`constraint-length-6,
`convolutional
`code;
`the
`decoder
`is a
`software-implemented soft-decision
`Viterbi
`decoding algorithm.
`The
`interleaving/
`deinterleaving system uses an interleaving depth
`of 16 symbols.
`This value was arrived at as
`a
`compromise between a sufficiently long interleav-
`ing depth to decorrelate channel interference and
`a reasonably short minimum message length. Using
`this interleaving depth and a block interleaver,
`the
`shortest
`allowable
`data
`link message
`is
`128 hits.
`while for most
`applications
`this is
`
`456
`
`BCJEINCB
`
`Ex.1031,p.517
`
`BOEING
`Ex. 1031, p. 517
`
`

`
`technique. However, for this application, modula-
`tion performances must be evaluated in the aero-
`nautical channel subject to phase noise and multi-
`path fading.
`
`The low-data-rate data
`
`The Phase Noise Problem.
`link application presents a design problem not en-
`countered in higher capacity systems.
`Phase noise
`generated by oscillators in the earth station and
`aircraft terminals, as well as in the satellite,
`seriously degrades the performance of PSK systems
`at low data rates. Coherent demodulation systems
`are more seriously affected by phase noise than
`are noncoherent systems, due to the degraded per-
`formance
`of
`the
`integral
`phase-tracking loop
`necessary in coherent systems. According to cal-
`culations performed using INMARSAT phase noise
`specifications and the assumption of a slow fading
`channel,
`the performance of BPSK becomes unaccept-
`able at channel symbol rates below about 350 bps,
`whereas DPSK is shown to perform adequately for
`symbol rates down to about 100 bps.[8]
`FSK sys-
`tems are the most resistant
`to phase noise, but
`this does not outweigh their
`power efficiency
`disadvantage in AWGN channels.
`
`Modem Performance in Multipath Fading.
`severe
`ulation performs better
`than DPSK when
`in a
`fading conditions are present.
`However,
`3 dB
`standard nonfading environment,
`it performs
`worse; and when coding and interleaving are used,
`FSK loses all of its advantages.[9]
`
`FSK mod-
`
`Multiple Access
`
`the multiple
`In a full-scale data link design,
`access
`system must
`accommodate as many as
`223
`aircraft that may be using the data link system at
`any one
`time.
`In the ground-to-air direction,
`the total channel capacity requirement
`(200 bps)
`is small
`enough
`to allow all users
`to share a
`common time-division multiple access (TDMA) chan-
`nel.
`A discrete,
`address-mode
`service would
`operate by including an aircraft address with each
`message
`transmission.
`Each aircraft
`terminal
`would have the capability of recognizing its own
`address, whereupon it would respond appropriately.
`
`The complexity in multiple access design is con-
`centrated in the air-to-ground link. First,
`it
`seems probable that
`the 700 bps
`total
`required
`air-to-ground channel capacity would be split be-
`tween four separate 200 bps channels,
`to form a
`time/frequency division multiple access
`(TDMA/
`FDMA)
`hybrid--essentially
`four
`separate
`TDMA
`channels.
`For a TDMA channel
`to operate in this
`multi-user aeronautical
`scenario,
`air-to-ground
`transmissions would either occur
`in response to
`ground-to-air polls or be very carefully timed.
`The earth station terminal must acquire the sig-
`nal carrier
`(the frequency of which is unknown
`due to Doppler and oscillator uncertainties)
`for
`each air-to-ground message
`transmission.
`This
`carrier acquisition must proceed quickly for the
`system to achieve the necessary system throughput
`performance.
`The
`experimental data
`link will
`demonstrate the use of
`an array-processor
`fast
`Fourier
`transform technique to quickly estimate
`the carrier frequency for fast carrier acquisi-
`tion on air-to-ground transmissions.
`
`Additional complexity is associated with air-to-
`ground message timing and arbitration.
`Each air-
`craft
`terminal must be
`synchronized to the earth
`
`457
`
`BOHNG
`
`Ex.1